1. Field of the Invention
The present invention relates to a self-centering timing disk hub with a timing disk support surface (1a) and a tubular hub sleeve (1b) and to a method for mounting the same on a motor shaft.
2. Description of the Related Art
Self-centering timing disks of the afore described type are known from DE 196 41 929 A1 (RUHLATEC Industrieprodukte GmbH). The timing disk hub described therein is installed in an encoder which is connected with a motor by a simple rotational motion.
Sufficient clearance should be provided for centering the timing disk hub on the motor shaft during installation. For this reason, the end of the timing disk hub facing the motor has a pilot bore for aligning the vertical axes of the shaft and the timing disk. With current state-of-the-art devices, a distortion tended to occur when the shaft is inserted into the timing disk hub, since the hub which is pushed onto the finish-machined shaft, has a reduced diameter. A housing surface exerts an axial pressure on the timing disk support surface, thereby moving the timing disk support surface and the timing disk hub connected thereto into the proper position for a centered placement in the encoder housing.
Such timing disks are used in an increasing number of applications and produced in large quantities. The stringent requirements on the surface quality of the motor shaft and the timing disk hub as well as the tight manufacturing tolerances create a cost pressure in mass production. It is also difficult to maintain the required tolerances in production. A slight displacement of the timing disk relative to the motor shaft can adversely affect the operation of, for example, servo motors. Manufacturing tolerances can have a significant effect due to the large forces applied during the pressing process.
It is therefore an object of the present invention to provide a self-centering timing disk hub which can be placed, and adjusted without pre-tension and secured on a motor shaft. It should be possible to install the timing disk hub installation in mass production, while maintaining the accuracy required for encoders.
According to the invention, a self-centering timing disk hub with a timing disk support surface and a tubular hub sleeve is provided. The sleeve end is being pushed onto a motor shaft with a contact surface being produced in the hub sleeve between the inner wall surface of the hub sleeve and the motor shaft. The outer wall surface of the hub sleeve is at least partially formed in the shape of a cone. The cone angle opens from the sleeve end to the timing disk support surface. The hub sleeve is slotted at least in the region of the motor shaft. A clamping element is movably arranged on the outer wall surface of the sleeve end. Further the cone angle is in the range of 10-15xc2x0 and the length of the at least one slot in the hub sleeve is in the range of 0.5-0.8 of the contact surface length between the hub sleeve and the motor shaft. The hub sleeve includes a stop face which defines the rest position of the clamping element, with the stop face located on the outer wall surface in a region of the open end of the slot. Further, the clamping element includes a clamping ring and may be manufactured of an elastic plastic material.
The at least one slot in the hub sleeve has a width of about 1-2 mm. In the first third of the hub sleeve, viewed from the side of the motor shaft, a locking face defining the tensioning position of the clamping element is machined circumferentially on the outer wall surface of the hub sleeve. The locking face has a protruding lip, disposed on the outer circumference of the hub sleeve. On the sleeve end on the side of the motor shaft, the inner wall surface of the hub sleeve has a conical enlargement. The conical enlargement on the inner wall surface of the hub sleeve extends from the end face over a range of 20% of the length of the hub sleeve. Preferably there are at least 4 slots within the hub sleeve of axis-parallel extension equally distributed on the circumference.
In addition, a method for mounting a self-centering timing disk hub on a shaft, in particular, a motor shaft of an encoder, is provided. The timing disk hub includes a timing disk support surface and a tubular hub sleeve, with the sleeve end of the hub sleeve oriented towards the motor shaft and the end of the timing disk hub facing the motor shaft is slotted with a clamping ring being pushed onto the slotted end. The clamping ring is then moved from a tension-relieved position into a tensioned position after the timing disk hub is shifted onto the motor shaft.
It has been observed that a timing disk hub formed according to the invention can be pushed onto the motor shaft and clamped at the time of installation, without displacing the timing disk axis radially or angularly relative to the motor shaft axis. Since during installation this does not produce a press-fit, only a relatively small force is required. Instead, the hub and the shaft slide relative to each other during installation and are changed to each thereafter only.